Re: qcow2 eating up space when formattng Centos

[Philipp Hahn <hahn@univention.de>]

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Hello Anonnymous,

On Monday 24 October 2011 03:22:15 day knight wrote:
> I am not sure if this is the right behaviour but qcow2 image seems to
> grow when Centos is only formatting the image. I mean it goes upto 30
> Gig once evrything is formatted and installed and it is minimal Centos
> install with no gui or apps just baseline.
>
> OS = Centos5
> Virtualization: KVM
> Total Qcow2 Image Created = 1TB
>
> Once Centos is installed the qcow2 image shows as around 30 Gig. I
> have done several install and they were all less than 4 gig or even
> lesser but this seems to not make sense
>
> Can someone please explain what is going on?

You didn't tell which file system you're using. ext3 needs to initialize its 
meta data (super blocks, inote tables), which are scattered all over the 
image. Depending on your cluster size fpr the qcow2 file, each (small) write 
takes the space of a full cluster. Add to that the meta-data needed by qcow2 
itself (a two-level tree), 30 GiB seem to be okay.

You might want to try ext4 with "delayed allocation" (IMHO enabled by 
default), which doesn't write all over the range, since initialization of the 
superblock and inode tables is delayed until they are acually needed.

Sincerely
Philipp
-- 
Philipp Hahn           Open Source Software Engineer      hahn@univention.de
Univention GmbH        Linux for Your Business        fon: +49 421 22 232- 0
Mary-Somerville-Str.1  D-28359 Bremen                 fax: +49 421 22 232-99
                                                   http://www.univention.de/

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